1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film spool.
2. Description of the Prior Art
As is well known, 35 mm film is supplied in cassettes ready for loading into a camera. The film is stored in a strip format coiled about a spool, and the spool is rotatably supported inside a lighttight cassette shell or housing.
The spool for the film cassette is shown in FIGS. 1 and 2 of the accompanying drawings. Specifically, it comprises a cylindrical hub or core 1 having a central cavity 3 which begins with an end opening 5 at one end 7 of the hub, and a split spline 9 forming a coplanar pair of identical spline pieces 11 and 13 fixed inside the central cavity 3. The two spline pieces 11 and 13 have respective flat ends 15 and 17 equally spaced from the end opening 5. See FIG. 1.
When the cassette is loaded into a camera, a rewind spindle comprising two depending prongs is intended to be inserted through the end opening 5 into the central cavity 3. As is the custom, the two spline pieces 11 and 13 are each received in a gap between the two prongs to rotationally couple the spindle and the hub 1.
Problems to be Solved by the Invention
One possible problem that can occur during insertion of the two prongs through the end opening 5 into the central cavity 3 is that respective pointed tips of the two prongs may each abut the flat ends 15 and 17 of the spline pieces 11 and 13 because the flat ends are equally spaced from the end opening 5. If the spindle is then rotated, the pointed tips of the two prongs might not be able to slip off the flat ends 15 and 17 due to the frictional relationship between the pointed tips and the flat ends. This will prevent the spline pieces 11 and 13 from being received in the gap between the two prongs to rotationally couple the spindle and the hub 1.
Another possible problem that can occur during insertion of the two prongs through the end opening 5 into the central cavity 3 is that the pointed tips of the two prongs may both be received in one of two cavity-halves 19 and 21, i.e. one side, of the central cavity 3. See FIG. 2. If the spindle is then rotated, either one of the pointed tips of the two prongs might not be able to hop over one of the flat ends 15 and 17 of the spline pieces 11 and 13 because the flat ends are equally spaced from the end opening 5. See FIG. 1. This will prevent the spline pieces 11 and 13 from being received in the gap between the two prongs to rotationally couple the spindle and the hub 1.